Institut Charles Sadron Event

The complexity of cell membranes is in part related to its composition, which includes a variety of lipids with different physical chemical properties. In in vitro studies using model membranes, we can group the salient properties of hundreds of lipids that compose the plasma membrane in different categories and study a mixture of a few components. To mimic the outer leaflet of the plasma membrane, a mixture of three lipid components, described as high melting lipid/ low melting lipid / cholesterol, forms coexistence of liquid phases, namely liquid disordered (Ld) and liquid ordered (Lo) phases. In the lipid raft hypothesis, specialized domains are important for different functions in the cell, such as protein sorting, signaling and virus assembling. Here, we characterize different properties of Ld/Lo domains as domain sizes, peptide partition and line tension. Besides the complex behavior of the plasma membrane outer leaflet, the plasma membrane inner leaflet (which faces the cytosol of the cell) has a completely different lipid composition, giving the bilayer an asymmetrical profile. In contrast to the outer leaflet, the inner leaflet lacks high-melting lipids and is suggested to form a single fluid phase. Recently, the bilayer asymmetry has risen important questions related to the coupling between inner and outer leaflets. Using asymmetric giant unilamellar vesicles prepared via hemifusion, we studied the influence of one leaflet upon another. In addition, a healthy cell maintains the balance of asymmetric leaflets, whereas, for instance, tumor cells have lipids from the inner leaflet flipped to the outer leaflet, an event that signals the cell apoptosis. For decades, antimicrobial peptides (AMPs) have been known to have anti-tumor properties. Interestingly, AMPs target the phosphatidylserine that is exposed to the outer leaflet in tumor cells. As a future direction, I plan to study the anti-cancer properties of AMPs in asymmetric bilayers.